INDLEDNING. 
Crustaceernes vidtloftige Classe inddeles, som 
bekjendt, ialmindelighed i to store Afdelinger, Mala- 
costraca, eller de hoiere Krebsdyr, og Entomostraca, 
eller de saakaldte Smaakrebse. LEnhver af disse 
Afdelinger lader sig igjen dele i 4 Grupper eller 
Ordener. Til den forste herer 1) Podophthalmata, 
eller de stilkoiede Krebse (Decapoda, Schizopoda og 
Stomatopoda), 2) Cumacea, 3) Isopoda og 4) Amphi- 
-poda; til den sidste: 1) Branchiopoda, 2) Ostracoda, 
3) Cirripedia, og 4) Copepoda. Hertil kommer endnu 
den i mange Henseender meget anomale, og i visse 
Punkter med Arachniderne beslegtede Gruppe, Xipho- 
suré, eller Dolkhalerne, som dog af flere Natur- 
forskere ikke henregnes til Crustaceerne, men be- 
tragtes som Typen for en egen Arthropodeclasse. 
Naar undtages denne sidste Gruppe, er alle de 
evrige ovenanforte Ordener vel repreesenterede i vor 
Fauna. For det forste vil vi alene komme til at 
beskjeeftige os med den forste af de til Entomostra- 
ceerne horende Ordener, Branchiopoda. Denne Orden 
har faaet sit Navn deraf, at et storre eller mindre 
Antal af de bag Munddelene felgende Lemmer an- 
tager en eiendommelig bladdannet Structur, der gjor 
dem fortrinlig skikkede til at fungere som Respira- 
tionsorganer, om de end i enkelte Tilfelde paa 
samme Tid kan fungere som Svemmeapparater. 
Undertiden, saaledes hos visse Cladocerer, kan disse 
Lemmers saavel respiratoriske som motoriske Func- 
tion vere meget reduceret, hvorimod de faar sin 
vesentligste Betydning som Griberedskaber, der 
understetter Munddelene ved at fastholde og bringe 
til Munden de Fodemidler, hvoraf disse Dyr lever, 
en Function, som imidlertid ogsaa for en Del kan 
paavises hos Former med forevrigt normalt udvik- 
lede Branchialfodder, f. Ex. Apus. Ogsaa hos fuld- 
1— G. 0. Sars: Fauna Norvegiz. 
INTRODUCTION. 
As is known, the extensive class Crustacea is, 
in general, classified into two great divisions viz., 
Malacostraca, or the higher Crustaceans, and En- 
tomostraca, or the so-called lower Crustaceans. 
Each of those divisions may be subdivided, again, 
into 4 groups or orders. To the first division per- 
tain: — 1) Podophthalmata or the stalk-eyed Crusta- 
ceans (Decapods, Schizopods and Stomapods), — 
2) Cumacea, — 3) Isopoda, and — 4) Amphipoda. To 
the second division pertain: — 1) Branchiopoda, — 
2) Ostracoda, — Cirripedia, and — 4) Copepoda. To 
them is added the Xiphosure, or sword-tails — in 
many respects very anomolous, and in certain cha- 
racters relat«d to the group Arachnida — which 
are by several naturalists, however, not assigned to 
the Crustaceans, but is considered to be the type 
of a special class af Arthropods. With the excep- 
tion of that last-named group all the other above- 
mentioned orders are well represented in the Nor- 
wegian Fauna. At present we shall only occupy 
ourselves with the first of the orders pertaining to 
the Entomostracans viz: Branchiopoda. This. order 
has obtained its appellation from the circumstance, 
that a larger or smaller number of the appendages 
behind the oral parts assume a peculiar foliaceous 
structure, which causes them to be admirably 
adapted to serve as respiratory organs, even although 
they, in a few cases, may at same time serve as 
swimming apparatuses. Occasionally, as in certain 
Cladocerans, both the respiratory and motoric func- 
tions of these appendages may be greatly diminished; 
and their essential importance becomes that of a 
prehensile-apparatus which aids the oral parts in 
securing and carrying to the mouth the nutriment 
upon which these animals feed; a function which 
